HMC Physics Colloquium

Theresa Lynn

Stargazing is perhaps one of humanity’s oldest pastimes. As modern astronomers have learned to image the universe in wavelengths across the electromagnetic spectrum, each added picture has answered old questions and uncovered new wonders.

In recent years a few observatories have concentrated on very different messengers from the cosmos: subatomic particles called cosmic rays which reach us from as nearby as the Sun and as far away as distant galaxies. The rarest and most energetic of these particles are called ultra-high energy cosmic rays, or UHECRs; a single UHECR proton can carry more than a Joule of kinetic energy. We know that UHECRs originate outside our own galaxy, but we remain puzzled by exactly what sources accelerate particles to such immense energies, and how distant these sources are.

CHICOS, an array of particle detectors at schools across the Los Angeles area, monitors ultra-high energy cosmic rays to determine their energies and look for clues to their origins. The rare particles we observe are messengers from some of the most violent activity in the cosmos, and could even provide hints of new physics at the smallest scales as well.